Transcript ISNR 2008 - Sterman-Kaiser Imaging Laboratory

Coherence and Comodulation:
Phase Synchrony and Magnitude Synchrony
David A. Kaiser, Ph.D.
Sterman-Kaiser Imaging Laboratory, Inc.
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ISNR 16th Annual Conference - San Antonio, Texas
August 28-September 1, 2008
Saturday Aug 30 9:10-9:30am
Functional connectivity and
neuroplasticity
Anatomy is destiny – Freud
Anatomy is merely a suggestion – Anatomy
Neural recruitment into larger functional groups
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Neurons fire around 80+ times a
second intrinsically (and up to 800
times a second during seizure).
To process information of relevance to
the organism, autorhythmicity is
greatly suppressed and firing
synchronized across neurons by means
of inhibitory and excitatory influences.
(Hopfield, 1999; Goldensohn & Purpura, 1963; Mountcastle, 1957; Casanova & Tillquist, 2008)
When autorhythmicity is suppressed in ~2,000,000 cortical
minicolumns (6 cm2), it can be detected by scalp electrodes.
Mountcastle, 1957; 1978; Cooper et al., 1965
Voltage rhythms correspond well
with mental and physical behaviors
Certain rhythms are generated by inhibitory networks
High information
STATE
Low information
Generation of spindles (7-14 Hz)
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Length of inhibitory potential sets the frequency (which is mediated by GABA
type A receptors) . The potential determines the time until another burst of
spikes is generated by the TC neuron (Franks, 2008)
The more neurons recruited into a rhythm,
the higher the spectral magnitude
Spectral magnitude = proportion of
neurons in the functional group
(rhythm)
Time delay between brain areas recruited into the
same function (rhythm) is indicated by phase
Detecting networks through
timing and number
Network organizes around event
Synchrony between sites as indicated by
phase and magnitude relationships
Phase and Magnitude consistency
Cross-spectral analysis
Coherence is a phase consistency function
Comodulation is a magnitude consistency function
…between signals at a frequency across time
Coh = average normalized cross-spectrum amplitude
Comod = average normalized cross-product amplitude
Coh
ranges from 0.0 to 1.0
Comod ranges from -1.0 to 1.0
Comodulation
Shared information between EEG signals
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Phase:
• Mean consistency
(coherence)
• Mean difference
(phase lag)
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Magnitude
• Mean consistency
(comodulation)
• Mean difference
(asymmetry, unity)
Functional Connectivity from 5 to 35 years of age
Four possible connectivity parameters
Normalizing with Fisher z-transform (1921)
Similarity of Coh and Comod
Kaiser, 2008 (n=43 children, 58 adults)
(Kaiser, 2008)
n =101
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Sowell ER, Peterson BS, Thompson PM, Welcome SE, Henkenius
AL, & Toga AW (2003). Mapping cortical change across the
human life span. Nature Neuroscience, 6, 309-15.
We used magnetic resonance imaging and cortical matching
algorithms to map gray matter density (GMD) in 176 normal
individuals ranging in age from 7 to 87 years. We found a
significant, nonlinear decline in GMD with age, which was most
rapid between 7 and about 60 years, over dorsal frontal and
parietal association cortices on both the lateral and
interhemispheric surfaces. Age effects were inverted in the left
posterior temporal region, where GMD gain continued up to age
30 and then rapidly declined. The trajectory of maturational and
aging effects varied considerably over the cortex. Visual,
auditory and limbic cortices, which are known to myelinate early,
showed a more linear pattern of aging than the frontal and
parietal neocortices, which continue myelination into adulthood.
Our findings also indicate that the posterior temporal cortices,
primarily in the left hemisphere, which typically support
language functions, have a more protracted course of maturation
than any other cortical region.
Left posterior temporal lobe has longest maturation (Sowell et al., 2003)
Effect of age on
connectivity
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Coherence increase with age (5-35 y, n=101)
Comodulation increases with age
Data are site-age correlations.
(pink is significant)
Functional connectivity in childhood
(5-20 years of age)
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Structural changes
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Functional changes
Functional connectivity in adulthood
(20-35 years of age)
Structural changes
Functional changes
College students show frontal plasticity compared
to older adults
Coherence
Comodulation
Role of myelin in cerebral connectivity
Without myelin sheath, 2 mph
With sheath, 260 mph
Biggest 5 micron
diameter “pipes”
are posterior but
big pipes
continue
frontally
throughout life
Corpus callosum cross-section
Functional connectivity in adulthood
(20-35 years of age)
Red areas are last to
myelinate
Functional changes
Global connectivity (alpha graphed)
Does phase and magnitude capture
different aspects of neurophysiology?
Scalp coherence may reflect RTN involvement in
cortical rhythms and comodulation the more
loosely organized corticocortical networks
Spectral parameters c.1994
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Absolute power
Power asymmetry (A-B)
Power ratio (A/B)
Relative power
Spectral entropy
Spectral Correlation
Coefficient (SCC)
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Coherence
Phase lag
Bicoherence
Spectral
Correlation
Same spectral parameters, organized
Bicoherence
Periodicity Table
(Kaiser, in press)
“Chemistry” between periodicity types